In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date part of common general knowledge, or known to be relevant to an attempt to solve any problem with which this specification is concerned.
Mass spectrometers are specialist devices used to measure or analyse the mass-to-charge ratio of charged particles for the determination of the elemental composition of a sample or molecule.
A number of different techniques are used for such measurement purposes. One form of mass spectrometry involves the use of an inductively coupled plasma (ICP) for generating a plasma. The plasma vaporises and ionizes the sample so that ions from the sample can be introduced to a mass spectrometer for measurement/analysis.
As the mass spectrometer requires a vacuum in which to operate, the extraction and transfer of ions from the plasma involves a fraction of the ions formed by the plasma passing through an aperture of approximately 1 mm in size provided in a sampler, and then through an aperture of approximately 0.5 mm in size provided in a skimmer (typically referred to as sampler and skimmer cones respectively).
A number of problems are known to exist with prior art mass spectrometer arrangements, which serve to reduce their measurement sensitivity. Various solutions have been proposed to address these problems. One such proposal is reported by Houk et al (‘Simultaneous Measurement of Ion Ratios by Inductively Coupled Plasma-Mass Spectrometry with a Twin-Quadrupole Instrument’, Applied Spectroscopy, Vol. 48, Issue 11, pp. 1360-1366 (1994)), where it is proposed to split a single beam of ions within an ion optics unit into two independent and diverging ion beam streams. However, a likely deficiency with the proposed arrangement is the high potential for ion losses to occur within the ‘splitting’ mechanism, in which low energy ions are deflected away from their intended path of travel while high energy ions impact the surrounding walls of the mechanism. For these and other reasons, the resulting spectrometric analysis based on this approach is unlikely to be acceptable in a commercial mass spectrometry device.